At age 75, she became the oldest to ever complete an Ironman and, at 82, she set the world record as the oldest Ironman triathlon competitor — male or female.

As well as extreme endurance races she has more than 370 total triathlons under her habit.

"I've learned other life lessons along the way,” Buder told Triathlon Inspires,

“But the ones that I'd look back and tell my twenty something self now are: It's not what you say, it's what you do; don't pay attention to how old you are, only focus on how old you feel.”

The American nun, from Spokane, Washington, loves the Ironman races each comprising of a 2.4-mile swim, 112-mile bike and 26.2-mile run.

Sister Madonna arrives at the finish line after Challenge Roth in Germany. (Image: Getty)

Her determined approach has earned her the nickname the “Iron Nun.”

Along the way she’s had some setbacks — missing a race finish by a matter of seconds, multiple broken bones, wetsuit issues — but, she proclaims, “The only failure is not to try, because your effort in itself is a success.”

She trains by running to church every day and bikes 40 miles to swim in a lake and eats plenty of raw fruit and vegetables as well as carbs and protein powder.

Sister Madonna regularly swims in a lake near her home (Image: Getty)

She's now the star of a new Nike advertisement where she is shown being put through her paces.

Sister Buder’s introduction to sport came just seven years before her first race in Hawaii, when she attended a workshop on the Oregon Coast that was led by a priest who championed running as a way to harmonize the mind, body and soul.

Sister Madonna Buder defies the usual constraints of her age

Sister Buder took this creed to the extreme, burning out on the sport before discovering the variety of the triathlon.

“That was the salvation,” she declares. Her physical endurance she attributes to listening to her body and maintaining a positive mindset.

The nun thinks nothing of hopping her bike for a 40 mile training ride

“You carry your attitude with you,” Sister Buder elaborates. “You either achieve or you self-destruct. If you think positively, you can even turn a negative into a positive.”

Along with this spiritual guidance, she imparts simple, yet easily applicable performance advice to younger athletes: “One step at a time makes a marathon.”

Sister Madonna on a training run in the new Nike advert

Sister Buder features one of a series of short films Nike has produced in celebration of a summer of sport, hailing everyday athletes and champion athletes who regularly push beyond the imaginable.

Are you a superfit pensioner or do you know one? Email steve.myall@mirror.co.uk